All language subtitles for S05E07 - Life and Death on the Red Planet.en

3.7 billion years ago,

early life was on the brink
of extinction.

Colossal impacts...

Ferocious climate change...

And total atmospheric collapse
have turned paradise into hell.

But this isn't Earth...

It's Mars...

And this is the violent
history of perhaps

the first life forms
in our solar system.

Could these martians
still exist today?

Could they even be
living among us?

Captions paid for by
discovery communications

scientists suspect that life may
once have thrived on Mars...

That the barren world
we see today

swarmed with martians long ago.

If I had to bet something
incredibly valuable to me...

If I had to bet my car...
On whether or not

there's life on Mars,

or evidence of past life
on Mars,

I'd take that bet.

The building blocks for life

are widespread in the universe,

and early Mars could have been
the perfect place

to pull these
ingredients together.

If you had a recipe book for
everything you need for life,

you'd have things like water,
organic chemistry,

a stable surface,
a thick atmosphere...

Well, Mars had
all of those.

Mars satisfies
every specific requirement

for letting life get started.

Life on Mars

may have been inevitable,

and we've sent a robot army
to hunt for signs of it.

But so far,
it's been elusive.

Our rovers, landers,
and satellites

haven't found life yet,

but they have found evidence
of something extraordinary.

Mars was the victim
of a devastating series

of extinction-level events

that rocked
the red planet to its core...

Leading us to wonder,

if life could have started over
multiple times,

with generation
after generation of martians

rising and falling through
Mars' violent history.

It seems likely
that a first Genesis of life

could have occurred very early
on in Mars' history,

just as soon
as the crust was cool enough

to give it a solid foothold.

The secret to this early life
would have been

a crucial ingredient,
one shared by the young Earth.

Dry, harsh Mars
once had oceans.

For life to get started,

you need some carbon,
an energy source,

it needs nutrients
like nitrogen...

But those are likely to be
present on Mars,

they are present
and widespread on Earth.

The essential requirement
is really the liquid water.

Picture Mars

4.5 billion years ago.

Molten rock has cooled
to form a solid crust.

Water collects on the surface,
forming primitive oceans.

Rain clouds sweep across

the steaming,
volcanic landscape,

and in shallow pools
of water,

the martians
begin to emerge.

But these first aliens
are simpler

than Sci-Fi
would have us believe.

We're probably not talking
about little green men

or women, or whoever.

Walking around on the surface
of Mars, we...

We're talking
about something probably

much, much smaller
and simpler,

single-celled life.

If would look familiar,

it would look just like
bacteria on Earth.

Little, tiny, round,
rod-shaped organisms.

If this generation

of bacterial martian life
really did exist,

it was the first life
to grace our solar system.

Multiplying inside
the rock pools of Mars

long before life
took hold on Earth,

Mars' small size would've
given it a head start.

Because Mars is smaller

than the Earth
it would have cooled

a little bit faster
than we did.

So early on in the life
of the solar system,

Mars may have been
more like Earth

than Earth was at the time.

Let's go back 100 million years

after the sun formed.

The surface of the Earth
is still a molten lake.

But martian life
could be thriving

on the smaller,
cooler world.

But these first martians
won't have long

to enjoy
their time in the sun.

Inescapable death is already
on its way from space...

A cosmic bomb so huge,

it would completely alter
the shape of the planet,

leaving it lopsided,

the northern
hemisphere crushed.

Most planets are round,

and that's just something
you don't really

give much thought to,

but it turns out Mars isn't
as round as it could be.

The Southern hemisphere,
on average,

has a higher elevation
than the northern hemisphere.

So, in other words, if you were
to start on the north pole

and walk all the way
around to the south pole,

you'd be walking uphill,
essentially, the whole time.

So, we call this difference
between the northern

and the Southern hemisphere,

we call this the crustal
dichotomy on Mars,

and it's been one of the biggest
mysteries of the planet,

you know, it's the first thing
that you see about it,

and you say, well, how could
this possibly have happened?

In 2008, scientists mapping

the surface of Mars came up
with an explanation

for the massive dent
in the planet, shown in blue.

This basin, the biggest
in the solar system,

had to be the result
of a massive impact.

Called the Borealis impact,

it blasted out a crater 6500
miles wide and five miles deep,

big enough to swallow
the entire United States

with room to spare.

Something really big happened.

In fact, the entire top half
of the planet

seems to have
practically been blown off.

The only thing that could do
that is a huge collision,

and we're talking a collision

with something the size
of Pluto, perhaps.

You're talking about an impact

that makes
the dinosaur killer impact

65 million years ago look pretty
much like a wet firecracker.

4.5 billion years ago,

the early solar system
is filled

with planetesimals
and protoplanets...

Asteroid-like leftovers
from a planet building process

that created Mars
and the Earth.

One of these
asteroids is huge,

and it's on a direct collision
course with Mars.

Any microscopic martians
have just seconds to live.

If this impact
was happening today

and we were so unlucky
as to be there to witness it,

what you first would have seen
is another moon in the sky...

And then you would've
looked back and seen,

oh, it's getting bigger.

As it came down it would have
filled the entire sky,

from horizon to horizon,

and as it struck,

the top would have still
been well out into space.

The impactor

is 1200 miles across,

the size of Pluto,

and as it hits,
the energy of the impact

shakes Mars to its core.

The entire planet
wobbles like jell-o.

As it came down,

it would have been hitting
into the surface of Mars

as fast as a bullet
out of a gun,

and it would have slammed
into the surface

and sent a shockwave out

that would've been bigger than
any earthquake ever recorded.

It would have been
like a Tsunami of rock

coming out and tossing us
out of the way.

The impact is catastrophic.

It blows nearly half
the planet's surface into space

and turns what crust remains
into a boiling lake of lava.

You can't have
an impact of that scale

without almost melting
the planet.

It's not literally
a planet breaking event,

but it's
a planet melting event,

and it is, it is
the sterilization

of the planet
at that point.

The surface of Mars was molten,

its atmosphere
blown into space,

the oceans boiled away.

If Mars was home
to the first generation of life

in our solar system,

that life didn't
stand a chance.

It would take the surface
of Mars 50 million years

to recover from the impact.

But what sort of planet
will rise from the ashes?

Compelling new evidence suggests
that the conditions for life

may have returned to Mars,

but did life itself
make a comeback?

This impact
was only a blip in time,

and there was possibilities
for life

and the planet to recover.

4.5 billion years ago

an asteroid
the size of Pluto

slammed into the surface
of infant Mars.

It melted the surface
of the planet,

it blew the atmosphere
into space,

and it boiled
away the oceans.

If life had gotten
a foothold on the planet,

that life would have been
completely exterminated.

But some scientists
believe this extinction

could have been brief,

and that life could have
started again from scratch.

One of the wonderful things

to imagine is that
there probably wasn't

a single origin of life.

It's not like
it happened once

and then everything
just went from there.

Maybe there were multiple times
that life got started

and went extinct.

Ten million years

after the Borealis impact

crushed the planet's
northern hemisphere,

Mars has cooled enough
for its surface

to become solid once more.

The planet has some
of the ingredients for life...

The right molecules,
a stable surface,

and an energy source.

But something's missing.

4.49 billion years ago
the surface of Mars was dry,

and without water,
life can't start over

and a second generation
of martian can never arise.

As far as we know life,

water is absolutely,
fundamentally important to life.

2004... NASA's opportunity rover

lands on Mars.

Part of its mission
is to search for evidence

that water returned to Mars
after the Borealis impact.

It's not long before
opportunity

stumbles across something
strange on the surface

of a fossilized sand dune...

Bizarre, round,
metallic rocks.

These rocks are called
blueberries,

and they're an important find
for planetary geologists,

like Jani Radebaugh,

because fossilized
sand dunes also exist on Earth.

And Utah's petrified dunes

are also littered
with blueberries.

This is really exciting

because we've seen the exact
same thing on Mars.

Finding blueberries on Mars

is significant,
because the Borealis impact

melted the planet,

so anything found
on Mars today

must have formed
after the impact.

But crucially,
these nodules of iron oxide

formed deep underground
and in the presence of water.

In order to form one of these
little blueberries,

there needs to be huge
amounts of water

flushing down
through the fossil sand dunes,

and as it does that,

it carries with it all
of the iron oxides

around each sand grain.

And just one tiny,
little one like this...

Now, this is maybe about

an ounce of iron,
maybe a little bit more...

And in order
to get an ounce of iron

to concentrate into
this blueberry,

you need to have
a thousand gallons of water.

Blueberries form

deep inside sandstone.

But over thousands
of years,

wind erosion blows away
the softer rock,

leaving just
the blueberries behind.

If we walk to the edge
of this

pile of blueberries,

we could see
the process by which

they're actually eroding
out of the rock.

The blueberries
right here contain

within this fossil
sandstone layer.

The winds are blowing
in this direction,

down the layers,

and they're actually eroding out
the soft sandstones right here

and leaving behind
very dense iron nodules,

and as they pluck themselves
out of the rock,

they roll down the hill
and they collect...

Right here,
in between layers.

We know we found conditions
just like this on Mars.

We have fossil
sand dune layers,

we also have blueberries
all over the surface,

so we know
the same kinds of things

had to have happened on Mars
that have happened here.

There has to be water
flowing through the rock,

gathering iron,

and then there has to be
a huge amount of wind

to strip away
the fossil sand dunes.

For blueberries to exist

on the surface of Mars today,

the red planet
must have gotten its water

and its atmosphere back after
the catastrophic impact.

With liquid water
on the surface,

the ingredients of life might
have combined, once again,

to create
a second generation of martians.

But where did this water
come from?

The answer is surprising.

It could have been
in the planet itself...

Water is incredibly abundant.

We know that
there's water deep,

deep, deep
in the Earth's mantle,

and so it's entirely
possible that on Mars

there was water so deep
in the planet

that even after this
catastrophe, it came back up.

On the Earth, scientists

diffuse the seismic waves
of earthquakes

to detect
an ocean's worth of water

chemically embedded
in minerals deep underground.

A similar water source
could have been hidden

hundreds of miles below
post-impact Mars,

and volcanoes could have brought
that water back to the surface.

One way for water to get from

deep underneath the surface
to the surface of the planet

would be through
geologic activities...

Volcanoes, for example.

We know that volcanoes spew out
a lot of gasses on Earth,

including water vapor,

and we see
volcanoes on Mars.

Mars is home to the largest

volcanoes
in the solar system.

The biggest of all,
Olympus Mons,

is over three times
taller than mount Everest.

4.49 billion years ago volcanoes
spew lava spiked with water

into the atmosphere
and create ferocious rainstorms

that flood
the surface of Mars.

Over tens of thousands
of years

Mars becomes
a watery world once again

with the perfect conditions
for a second generation

of martians to rise up.

It would seem that

when you have
a massive collision,

like what happened to Mars,

it would be game over
for life.

But there's something
more complicated going on.

Maybe that asteroid impact
kicked off

an entirely new cycle
of life on Mars.

In theory,

four billion years ago,

a second generation of
single-cell bacterial life

arose on Mars,

and for the very first time
there was life

on two planets
in the solar system.

140 million miles away,
life on Earth had just begun,

and thanks to Earth's
stable climate,

it would one day
evolve into us.

But the outlook for Mars
was very different.

Evidence from the Mars
reconnaissance orbiter

suggests an icy apocalypse
was about to strike.

For Mars' second generation,
winter was coming.

Four billion years ago,

the first life
has arisen on Earth,

but on Mars, life may be
starting out for a second time.

It's possible that Mars

had life before Earth did...
It got wiped out...

And then got started again
by rehydrating the planet.

A planetary collision

has blown away Mars'
atmosphere and oceans,

along with any life,

but giant volcanoes have brought
water back to the surface

from deep within the planet.

This could have allowed

for a second generation
of life to rise up.

But these martians are about
to be tested to their limits

by catastrophic
climate change.

2008... NASA's Mars
reconnaissance orbiter

flies high
over the surface of Mars.

Its ground-penetrating
instruments

peer deep below the surface,

aiming to unlock Mars'
geological secrets.

As it scans
near Mars' equator,

the orbiter spots something
that has no right to be there...

A vast,
underground glacier.

One mile thick and three times
the size of Los Angeles,

ice on this scale should
only form at the frigid poles.

The only explanation...

Mars must have been
tipped over

with its equator
tilted away from the sun.

The tilt on Mars' axis

has actually changed
significantly over time,

and in non-systematic ways,

it just happens randomly
that it will start moving,

and so there are some
models that suggest

that Mars has actually been
almost tipped over on its end.

Most planets wobble,

and from time to time,
they wobble so much

they can tip over,
leading to super winters.

If that had happened
here on Earth,

Los Angeles
could become the arctic.

Well, you can imagine something
similar would happen on Mars,

how drastic the change
would be.

You're used to seeing
the sun overhead,

it's very warm,
there's probably liquid water,

and as the planet
starts going this way,

the sun is not gonna rise
as high in the sky.

Eventually you may not see
sunrise for half a year,

and any water that's
there is gonna be frozen solid.

3.9 billion years ago,

Mars is tilting
by as much as 80 degrees.

Winter temperatures drop below
minus 125 degrees Fahrenheit.

As the polar ice sheet spreads
quickly toward the equator,

liquid water is frozen solid,

along with any potential
martians.

The water that drives
the biochemistry of life

freezes inside
the tiny bacteria.

Ice crystals form and puncture
the martian's cell walls

until eventually, they die.

Every 120,000 years
the tilt of Mars changes,

as again and again
the planet's chaotic wobble

flips the martians in and out
of the deep freeze.

Any second generation
of life on Mars...

Is left in tatters.

Meanwhile, on Earth, our ancient
ancestors have it easy.

The Earth's wobble, and its
seasons, stay relatively stable,

and it's all thanks
to our secret weapon...

Our oversized moon.

The interaction
of our planet and the moon

means that the axis of our
rotation is very, very stable.

The seasons return year after
year, century after century,

for billions of years.

Our moon's enormous mass

exerts a huge gravitational pull
on the Earth,

stabilizing the wobble
of our planet

and keeping
our climate in check.

Without the moon,
the early Earth

would have wobbled
just as wildly as Mars,

and our ancestors could have
faced the same icy fate

as the early martians.

Mars doesn't have a big moon,

it has two, little,
tiny moons

that don't really
affect it much.

So if the martians were killed

the first time
by a giant impact,

they may have been killed
a second time

by Mars itself not being
stable and flipping over

and having catastrophic
super winters and super summers,

basically, mega catastrophic
climate change.

On Mars, the outlook for life

seems bleak.

But the brutal conditions
that drive martian life

to the edge of extinction
may also have pushed it

to adapt and evolve.

We know this because on Earth
organisms known as extremophiles

have evolved to live in the most
severe of circumstances,

from boiling,
hydro-thermal vents...

To the deep freeze
of glacial ice.

When the going gets tough,
life seems to get tougher.

Maybe the martian
super winters

gave rise to
a third generation of life...

A super tough army of bugs
able to survive

the harshest
of climate swings.

What we see on Earth
is that life evolves

to occupy
whatever niche it lives in,

and that evolution takes time.

So as the environment changes,
life changes with it.

If there are sudden changes,

then life forms can't cope
with it and many die away.

Those that survive,
they continue on.

3.8 billion years ago

a third generation
of life could have thrived

on the surface of Mars.

Evolved from a handful
of its predecessors

to make it through
Mars' super winters,

it's the toughest
martian life yet.

But, as the super winters end,

the challenges for life
on Mars are set to get worse.

Another extinction-level event
is on the way.

Mars' atmosphere is being ripped
away molecule by molecule.

Could this be the killer punch

that wipes out
the martians for good?

Narrator: Imagine Mars

3.8 billion years ago.

It's a warm, wet world,

and super tough bacterial life
is thriving.

But these martians are not
the planet's first inhabitants.

The first generation
of martian is vaporized

by the huge Borealis impact.

Perhaps life starts over
from scratch,

but endures a series
of extreme climate swings.

Only the toughest martians
make it through.

But another disaster
is about to strike,

and this catastrophe will test
even the strongest martians.

They're about to lose the most
basic ingredient of life...

Liquid water.

You really have to appreciate
how difficult it is

to have liquid water
on the surface of a planet.

We know that life works
so well

when there's
liquid water around.

But you need
just the right balance

of air pressure
and temperature.

Without air pressure

weighing down on it,

liquid water will evaporate from
the surface of a planet,

whatever the temperature.

That air pressure
is generated

by the presence
of an atmosphere.

In a lot of ways that atmosphere

serves as a kind of a lid

stopping down the water
from escaping into space.

It's very important
to have that atmosphere.

3.7 billion years ago,

life on Earth enjoys warm oceans
and a thick atmosphere.

But on Mars,
a third extinction-level event

is gaining momentum.

The atmosphere is slowly
being stripped away,

and Mars' great oceans
are starting to evaporate.

The fate of life
on both planets

now rests on the strength
of their magnetic cores.

It turns out
that the existence

of an atmosphere on Earth may
rely on the magnetic field,

because what
our magnetic field does

is it protects us from
the onslaught of this wind,

of subatomic particles

that the sun is blowing out
all the time.

We call this the solar wind.

And if we didn't
have a magnetic field

to basically catch and deflect
those particles gently,

they would directly slam
into the Earth's atmosphere.

If you think
of the magnetic field

as a windbreaker
from the solar winds,

once we lose that protection,

that planet becomes
very vulnerable.

The Earth's magnetic core

has stayed strong
for 3.45 billion years

as super hot molten iron
churns over and over

within the planet
like a lava lamp.

Churning iron
creates electricity,

which in turn generates
a magnetic field

that rises up around the Earth,
acting like a magnetic shield,

protecting our atmosphere from
the ravages of the solar wind.

3.8 billion years ago

Mars had a molten core
and a magnetic field.

But something caused
its shield to drop.

Did Mars' small molten core
simply get too cold to function?

Or did
something else kickstart

this third great extinction
of martian life?

A new and controversial
theory points the finger

partly at
the ancient Borealis impact.

A giant impact of this scale

can affect a range
of temperatures,

from the hot inner core
to the cooler outer mantle.

4.5 billion years ago

the impact that vaporizes

the first generation
of martian life

also drives heat
into the planet,

increasing the temperatures
in the outer mantle.

The heat inside the planet
evens out,

and the metals
slowly stop churning.

But there's less
of a temperature gradient...

That makes it harder
for this dyno process to,

to drive a strong
magnetic field.

Over hundreds of millions

of years, Mars' magnetic field
shuts down.

When Mars lost its magnetic

field all of a sudden

it was completely
vulnerable to the solar wind.

The solar wind
could break apart

and carry away
the martian atmosphere.

3.7 billion years ago

super tough martian life
faces annihilation.

Bit by bits, the atmosphere
is being swept into space.

The air pressure
is dropping across the planet

and most of Mars' water
has already boiled away.

The chances of survival

without this precious liquid
are remote.

But, for the martians, there's
an even more immediate danger.

With no magnetic field
and no thick atmosphere,

the surface of Mars
feels the full force

of the sun's radiation.

If you're a microbe

on the surface,

you would
have to make do

with very little atmosphere,
no water,

this flood of ultraviolet light
from the sun,

and these particles which are
slamming into you all the time.

The martians are bombarded

by radiation
from the solar wind.

It rips their DNA apart.

Without an atmosphere,

the surface of the planet
is sterilized.

But is this really
the end for martian life?

Life is so tenacious,

it can survive even those
incredible catastrophic changes,

and it may still
be there today.

To survive the radiation,

martian life would have had to
have moved deep underground.

In this protected
subterranean environment

it may also have found
a source of liquid water,

and if that happened,

could the martians
still be there today,

waiting for us to drop in
and say hello?

Since the 1960s

robotic probes and landers

have been searching the surface
of Mars for signs of life.

But have they been looking
in the right places?

The surface of Mars
is a waterless desert

that's bombarded
by harmful radiation.

If a fourth incarnation of
martian life is alive today,

many scientists think it'll
have to be deep underground.

Underneath the surface of Mars

you may have all the conditions
you need for life.

There may be some liquid water
down there,

and you're also protected
from the intense radiation

that you find on the surface.

Scientists are split

on the best underground places
to search for martian life.

But if Jani Radebaugh
were on Mars,

she would head to the nearest
sand dune and start digging.

Here you can see

this is wet sand
just below the surface.

This is the perfect environment
to be able to house life.

Even in the very driest
deserts on Earth,

in between the sand dunes,
in the inter-dunes,

you can find water
percolating up from Springs

that come up from
deep under the ground,

perfect for life
to form and grow.

And if you just keep on
digging...

Down into the bottom
of the inter-dune,

maybe you would reach
the water table.

And if you reach
the water table on Mars,

now you have all the conditions
just right for life.

This is my bet,
this is where I'd go,

right between the dunes.

Digging for martian life

in the desert is one option.

But some scientists
have very different ideas,

and planetary scientist
Nina lanza

would need to pack a rope
and a flashlight for her search.

So if were to go to Mars
to find life,

I would go to a lava tube.

Lava tubes are made

by ancient volcanoes,

the empty leftovers from
underground lava flows.

Today,
they form deep tunnels,

shielded from radiation
and shut off

from the harsh
martian climate.

We've never been

in a lava tube on Mars,

but it is absolutely possible
that there's liquid water.

So, that's an environment where
you could have some moisture,

you could have a little warmth,
you're protected from radiation.

I think that a martian microbe
would be very happy there.

Finding life on Mars

would be a monumental
human accomplishment.

But there is a danger.

By exposing martian
life to life from Earth,

could we unwittingly set off yet
another extinction event?

Humans have been

one of the most effective
extinction mechanisms

of life on Earth.

The interesting
question will be,

will we produce a similar
calamity on Mars?

If humans someday
go to Mars,

then we will be
an invasive species,

and if there is some
martian life

that's hanging on
in some niche,

we could be
their ultimate destroyers.

So we have an ethical
responsibility

to preserve whatever
life may be on Mars.

The problem isn't us,

it's the bugs
in and on our bodies.

The average human has

ten to 20 trillion
bacterial hitchhikers.

If we go to Mars,

we'll be taking our tiny
companions along for the ride,

and any one of those bugs
could turn out to be

a deadly competitor
for martian life.

It's NASA engineer
Moogega Cooper's

job to keep
Mars rovers bug-free.

But keeping astronauts clean,
that's a whole different matter.

We bake our spacecraft hardware

at 110 degrees Celsius
for at least 50 hours

to prevent the contamination
of Mars.

But unlike spacecraft,
we cannot bake humans out.

We will not survive
those temperatures.

Unless we find a way

to keep astronauts bug-free,

exploring Mars with robots
is our best option

for keeping the martians
safe from harm.

But what will happen
when our robots

finally find that life and we
look deep into the workings

of our extraterrestrial
neighbors?

What will the martians
turn out to be like?

Our example where DNA
is the organic molecule

that carries
the information of life...

We don't even know

if that's gonna be
the rulebook in other places.

Finding any evidence
whatsoever on Mars

would help us better understand
what else is possible.

Will the martians

be different than us?

Made from
different materials

and with a different
biochemistry?

Or will they seem
shockingly familiar?

Some scientists think
that the very first martian life

may not have stayed on Mars.

It may have come here.

It's not that
farfetched to think

that life could have
jumped from Mars

or been a back and forth
from Mars to Earth.

If the martians came to Earth,

could they have seeded life
on our planet?

Maybe the martians aren't dead.

Maybe I'm a martian,
maybe you're a martian.

We've sent a robot army to Mars,

and what it's found
is astonishing.

The possibility that life
could have arisen there,

perhaps more than once,

with different generations of
martians emerging from the ashes

of catastrophic
extinction events.

Life could still be sheltering

below the surface of Mars
right now.

But there's another possibility
that's truly astounding...

That martians
aren't just hiding out on Mars,

they're thriving,
right here on Earth.

I might be a martian,

you might be a martian.

We might be from another planet.

We might have already travelled
and lived on two planets

as life forms...
Not as a species, certainly,

but our ancestors may have
come from another planet,

and that is mind blowing.

The idea that our ancestors

could be martians
is a new take on an old theory

called Panspermia.

According to the theory,

life on Earth began
when a space rock

filled with alien bacteria
landed on the Earth

and every living thing
we see today, including us,

evolved from those
cosmic hitchhikers.

The idea of Panspermia
has been around for centuries,

but had a resurgence
when scientists

determined that life on Earth
may go back four billion years,

to the end of a sustained
attack of asteroid showers

known as the late heavy
bombardment.

There are a lot of objects
from the outer solar system...

Comets and asteroids,
all kinds of things...

Coming into
the inner solar system

and slamming
into the planets.

Conventional wisdom

suggests the objects
hitting the Earth at the time

were leftover debris

from the formation
of the solar system.

But a very controversial idea

suggests these space rocks were
actually all pieces of Mars,

thrown off
in the Borealis space impact

when a huge object
blasted into Mars.

The timing links up really well
for the Borealis space impact.

If you calculate
how much debris

that would have been
thrown out into space

and when it would have
had to have happened,

according to the martian
geologic record,

it coincides with
the late heavy bombardment...

It's possible
that the debris

from the Borealis
space in forming impact

might have come to Earth
and rained down on us

and made the late heavy
bombardment,

seeding the Earth with
bacterial spores from Mars.

Now, this is just a hypothesis,
we don't know this for certain,

we don't have evidence.

But it is physically possible
for that to have happened.

Was the Earth seeded

by microscopic martians

blown into space
by the Borealis impact?

It sounds crazy,
but the science stacks up.

We know that simple life
is tough,

able to survive
in the cold vacuum of space,

and the timing
of the Borealis impact

works out well for the rise
of the first organisms on Earth.

Crucially, we know that rocks
ejected from Mars

can make it
all the way to Earth

because they're still
crash landing here, even today.

One of the coolest things
I've done as a scientist

is held a piece of Mars
in my hands.

Now, we never had a mission that
returned a sample from Mars,

we had to come about it
a different way.

And it turns out
we have meteorites

that we are 100% sure
are bits of Mars.

They were actually exploded out
during huge collisions,

and eventually
they fell on the Earth.

Four different generations

of martians,
each of them facing

a different planetary
catastrophe.

But despite enormous odds,

martians could
still be alive today,

buried deep under
the surface of Mars,

or maybe even
thriving on Earth.

If life is really that tenacious

that it can come back
and keep coming back

and keep coming back,

that gives me a lot of hope
for life in the universe.

That tells me that life
is maybe tough,

maybe individuals are fragile,
but maybe life itself is tough.

For now,

all we can do is speculate

until future generations
develop the technology

to visit the red planet

and grab our first sample
of extraterrestrial life.

That's going to change
everything.

We're going to have
another example

of how life started
and how life works.

And even if it's something
that's dead,

we knew it was there.

The universe will never be
the same again.